The present invention relates generally to improvements in the art of marine propulsion and, more particularly, to apparatus for vertically positioning outboard motors on the transoms of boats.
For maximum efficiency of operation, an outboard motor should be mounted on the transom of a boat such that the cavitation plate of the motor runs across the surface of the water while the boat is being operated. At such a height, the cavitation plate will be appropriately positioned to carry out its function of preventing air from reaching the propeller area, thereby preventing cavitation or slippage of the propeller in the water that can reduce the efficiency of operation of the motor, while, at the same time, the water will produce only a minimal drag on the motor to be overcome by the motor during the operation of the boat.
While this criterion for motor positioning has long been known, practical problems have in many cases prevented the criterion from being met, especially where a boat may be used for a variety of purposes. For example, an appropriate height setting for the motor where a boat is to be used as a work boat, operating at relatively low speed but requiring maximum thrust, is generally such that the cavitation plate will be positioned one to three inches higher than the bottom of the boat. This same setting, however, would not be appropriate where the boat should, at some other time, be used for racing purposes. At the higher speeds involved in racing, the stern of the boat is lower in the water requiring a setting of the cavitation plate generally of the order of three to five inches above the bottom of the boat to prevent excessive drag and to permit maximum speed to be obtained with propellers designed especially for racing purposes.
While the motor can be secured to the transom at different heights at different times to adjust for different uses to which a boat may be put, a practice that has occurred in the past, such solution to the problem is not only inconvenient and time consuming but introduces further problems. For example, where a boat is to be used for racing, mounting the motor at a height appropriate for conditions existing during the race results in a very low starting thrust for the motor so that the price paid for maximizing efficiency at high operating speeds is excessive time required to reach such speeds.